Effect of Pu content on uncertainty in reactor parameters due to use of no
temperature gradient in (U-Pu)O$_{2}$ fuels

Authors:
MEHMET TÜRKMEN

Abstract:
Radial temperature distribution in a fuel rod is a
parabolic function. Neutronics calculations are in general performed over a
volume-averaged temperature by ignoring this distribution. Such an
assumption results in an uncertainty in reactor design parameters. In this
study, the magnitude of this uncertainty is estimated by solving the heat
equation with a temperature-dependent conductivity coefficient coupled with
a reactor physics code. The effect of radial fuel temperature distribution
is investigated by representing the fuel region as multiregional.
Uncertainty is investigated for various Pu contents of (U-Pu)O$_{2}$ fuel, a
mix of depleted U and reactor-grade Pu. The effect of Pu content on the
uncertainty is studied. The PWR TMI-1 unit cell case from UAM test problems
is used in the calculations. Results are obtained by using the discrete
ordinate method. From the results, it was observed that uncertainties in
reactor parameters ($k_{\infty }$ and Doppler coefficient) due to the
use of no temperature gradient and in $k_{\infty }$ due to
cross-sections decrease as Pu content increases. Moreover, it was
calculated that uncertainty due to uniform temperature inside the nuclear
fuel is about 7% of uncertainty due to cross-sections.